解决挤出机口模流涎和积垢问题

STOPTHOSEDROOLINGDIES解决流涎口模问题上海北京顺德翻译文章来自于塑料产业论坛（）上海北京顺德手机：[phone]；emil：[e-mail]:PlasticsTechnologyIssue:November2012Diedrool,orplateout,cancauseahostofproblemsforextrusionprocessors.Hereishowtostoptheproblembeforeitstarts.口模流涎或者叫模垢，可能对挤出加工者引起很多问题。本文就是解决这些问题的方法。ClickImagetoEnlargeFig1.Along-landdiecontrolsthermoplasticswelltoanormalrange,drawingdownintoasizer.图1长通道口模将热塑性塑料的出口膨胀控制在标准范围内，然后牵引进入定径套Fig2.Here,thermoplasticswellisexcessiveandimpingesontheouterdielip,causingdiedrool,showncloseup(inset).热塑性塑料出口膨胀严重，对外模唇有不良影响，引起口模流涎，如近镜头所示。Oneextrusionprocessorwasemphatic（强调的）tomeaboutit:“Ifyouextrudeolefinicorthermoplasticelastomericcompounds,”hetoldme,“youwillexperiencethediedroolproblem.”一个挤出加工者对我强调说：“如果你挤出聚烯烃或者热塑性弹性体共混物，你可能会遇到口模流涎问题。”He’sright.Itdoesn’tmatterifyouareextrudingsheet,film,pipe,tubes,orprofiles—youcancomeface-to-facewithdroolingdiesinanyoftheseprocesses.他是对的。但是，不要紧。如果你挤出片材、膜、管、软管或者型材---你可得在任何这些工艺中面对口模流涎问题。Diedroolshowsupasabuilduponthedielips.Thisbuildupcaneitherbethesamecolorasthematerialbeingextruded,orinsomecasesappearsyelloworred.Oftenthisbuildupwillcreateunacceptablemachine-directionlinesintheextrudate.Andafteraperiodoftimethisbuildupwillultimatelybreak-offandattachitselftotheextrudate,resultinginadditionalaestheticflaws.口模流涎显著表现为模唇堆料（堆积）。这种堆积物可能与挤出材料的颜色一样，在某些情况下也可能是黄色或红色的。这些堆积物常常沿着流动方向在挤出物上划出不可接受的纹道。过了一段时间后，这些堆积物会最终破碎并附着到挤出物上，最终引起额外的美学缺陷。Diedroolisalsocommonlyreferredtoasplateout.Tofindtherootcauseoftheproblem,you’llneedtoanalyzethe“bigthree”areastoidentifywhat’stoblame（归咎于）:口模流涎常常也叫做积垢。为了找到问题的根本原因，你需要分析三大板块，以确定要归咎于什么原因：•Material:Eachthermoplasticisunique,withcompoundedalloysbeingthemostproblematic.Compoundedthermoplastics(thosethathaveadditivescombinedwiththebaseresin)havethehighestprobabilityofadditivesexuding,alsoknownasmigration.Forexample,inrigidPVCcompounds,thereareinternalandexternallubricants,typicallylow-meltingwaxes,whichcanmigrateoutofthematerialmatrix.Alongwiththeseconstituents,plasticizersareaddedtomakePVCflexible;thesearealsopronetomigrationwhencriticalshearratesareachieved.材料：每种热塑性塑料都是独特的，共混合金是最蛋疼的品种。共混热塑性塑料（挤出树脂＋助剂）具有助剂析出的最大可能性，助剂析出也称为迁移。例如，在硬PVC共混物中，添加有内外润滑剂，一般是低熔点蜡，它们会迁移到基体材料的表面。在这些组分中，还有增塑剂也添加到PVC中以增加PVC柔性。当达到临界剪切速率时，这些助剂都有析出倾向。Reactorgradesofolefinicpolymerssuchaspolypropyleneandhigh-,medium-,orlow-densitypolyethylenearelessproblematic;however,theystillcanbethebane（灾星，祸害）oftheprocessor.Manyolefinicthermoplasticsareacombinationofdifferentmolecular-weightgradestoachievecertainphysicalcharacteristics.Theresinsuppliercanblendhigh-molecular-weightresinwithalowmolecularweighttoincreasethemodulus(stiffness),andathighshearratestherecanbemigration,leadingtodiebuildup.However,onpolyolefinsandnon-compoundedthermoplastics,therootcauseofdiebuilduptypicallyisnotmaterial-related,sofurtherinvestigationwilllikelybenecessary:反应器牌号的聚烯烃，如聚丙烯和高、中、低密度聚乙烯较少有问题。但是，它们仍然可能成为加工者的灾星。许多聚烯烃热塑性塑料是不同分子量牌号的并用，以求达到某种特性。树脂供应商可能用低分子量树脂掺混高分子量树脂，以提高模量（刚性）。在高剪切速率下，低分子量树脂可能迁移，导致口模积垢。但是，对于聚烯烃和非共混热塑性塑料，口模积垢的根本原因一般不是与材料相关的，所以进一步的研究是必要的。•Machine:Thenextareatoanalyzeistheextruder.Itisimportanttoknowthephysicalconditionofyourextruder,especiallythebarrelandscrew.Excessivescrewwearorevenmoderatebarrelwearcancauseproblems.Barrelandscrewwearareproblematicbecauseasingle-screwextruderisnotapositivepumpingdevice,andanywearreducesoutput,requiringahigherscrewspeedtomaintainthedesiredrate.Higherscrewspeeds,inturn,leadtoadditionalfrictionalheatimpartedtothethermoplastic,causingameltseparationanddiedrool/buildup.机器：接着要分析的一个版块是挤出机。最重要的是要知道你的挤出的实际条件，特别是机筒和螺杆。过分的螺杆磨损甚至是中等的机筒磨损都能引起问题。机筒和螺杆之所以引起问题，是因为单螺杆挤出机不是一个正向泵送设备，任何磨损都减少产量，从而要求更高的螺杆转速以维持所要求的产率。反过来，较高的螺杆转速又导致额外对热塑性塑料有害的摩擦热，最终引起熔体分离和口模流涎/积垢。•Tooling:Toolingdesignplaysanimportantroleinthedie-droolproblem.Thetwokeydesigncriteria（指标）aredrawdown（牵引）andlandlength（通道长度，指螺杆末端到口模外表面的长度）.Butbeforeeventhinkingaboutdiedesignyoushouldinspecttheconditionofthedielip.Dielipsshouldbesharpand“dressed”(deburred)toa0.25-mm(0.010-in.)edge.Iftheedgehasalargerradius,say0.75mm(0.030in.),materialcanbuildupinsidetheradiusandcreateanareathatwillleadtocontinueddiedrool.Theaestheticflawwillexhibititselfintheformof“smearmarks”ontheextrudate.Onthematterofdesign,drawdownandlandlengthareinseparableparameters.Theyareamainrootcausefordiedrool,butprobablytheleastunderstood.Tobestunderstandtheirinter-relationship,let’sreviewthemindetail:成型加工设备：加工设备在口模流涎问题上起重要作用。两个关键设计指标是牵引装置和通道长度。但是，在考虑口模设计之前，你应该检查模唇的状况。模唇应该是平直的，倒角到0.25mm。如果倒角半径较大，比如说0.75mm，材料可能在半径内积垢，出现一个连续流涎的区域。外观缺陷表现为挤出物上出现污痕。Drawdown:Thesizeofthedesigneddiedimensionsindeferenceto（根据，依据）thefinalpartdimensions.Thedimensionalratioofthedietofinalpartusedtooffsetthe“swell”ofthethermoplasticasitexitsthedie.牵引装置：根据最终部件的尺寸来确定的所设计口模的尺寸。口模尺寸对最终部件尺寸的比例用于抵消热塑性塑料挤出口模时的“膨胀”。Landlength:Thelengthofthesteelthatrunsparalleltothepolymerflow.Theland-lengthratioistheratioofthelandlengthtothediegap(wallthickness).通道长度：平行于聚合物料流方向的钢的长度。通道长度比是通道长度与口模间隙（壁厚）的比例。Alsobemindfuloffourequallyimportantfacts:还要注意以下四个同样重要的事实：1.Short-landdiesexhibitgreater